FM (Frequency Modulation) systems are used, especially in classrooms, to improve the signal-to-noise ratio during the transmission of signals to hearing devices. In such cases the teacher generally wears a microphone with a transmitter and the students wear a receiver, with a connection to a hearing device where appropriate. If the teacher leaves the room and forgets to switch off the microphone, the students can listen in to conversations, taking place in the staff room for example. The teacher must thus attempt to avoid not switching off the microphone manually at the right time.
An FM multifrequency system for schools made by Phonak is known. In this system the receivers in a classroom are set automatically to a configured radio frequency. A change of classroom automatically changes the frequency at the receiver.